The present invention relates to a fiber reinforced metal type composite material, and more particularly refers to a fiber reinforced metal type composite material in which the reinforcing fiber material is alumina fiber and the matrix metal is a light metal such as aluminum, magnesium, or an alloy of one of these.
Various elements and members of various machines are required to have particular mechanical properties in various of their portions. For example, when two mechanical parts or portions slide on one another in rubbing frictional contact, it is required that good strength and rigidity of the mutually contacting portions should be available, together with superior anti wear characteristics of the mutually contacting portions. As one method of improving the strength and rigidity characteristics of such mutually contacting and rubbing portions, and of improving the anti wear characteristics thereof, it has been conceived of, and put into practice, to construct these mutually rubbing and contacting portions of composite material using reinforcing fibers within a matrix of matrix metal, which is usually a light metal such as aluminum or magnesium.
One known such fiber reinforced metal type composite material uses alumina/silica fibers as the reinforcing fiber material and aluminum, magnesium, or alloys thereof as the matrix metal, and using this fiber reinforced metal type composite material it is possible to substantially improve the strength and anti wear characteristics of elements made therefrom which are subject to rubbing frictional contact. However, a problem that has arisen with such composite materials using alumina/silica fibers as the reinforcing material is that, because the alumina/silica fibers are very much harder than the aluminum or magnesium matrix metal, the members which bear against and rub against the parts made from such a composite material made of alumina/silica fibers and aluminum, magnesium, or an alloy thereof as matrix metal tend to be worn away quickly. Further, machining of the composite material is also very difficult. These problems are particularly prominent in the case of a composite material using alumina/silica reinforcing fibers which are more than about 80% by weight composed of alumina, with the remainder silica, although from the point of view of having high compatibility with aluminum alloys and the like and superior heat resistance characteristics these high alumina type alumina/silica reinforcing fibers are preferable.
Now, various different crystalline structures exist for alumina. In particular, of these so called alpha alumina is the most stable one, and is known already to have high hardness and elasticity. For example, so called alumina short fibers, which are currently sold as a heat resistant material, commonly have an alpha alumina proportion by weight of 60% or more, i.e. the ratio of the amount of alpha alumina present therein to the total amount of alumina present therein is 60% or more. Thus, it would be expected and has been formerly considered that: the higher is the proportion of alpha alumina present in the alumina of the alumina/silica reinforcing fibers of a composite material including alumina/silica fibers as reinforcing material and aluminum, magnesium, or an alloy thereof as the matrix metal, the higher are the mechanical strength, the rigidity, and the resistance to wear of rubbing elements made from said composite material; but also the higher is the amount of wear on a mating element which rubbingly mates against said rubbing element made from said composite material, which is highly undesirable; and also workability of the composite material is decreased.